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Semiconductor gas sensors using metal oxides, carbon nanotubes, graphene-based materials, and metal chalcogenides have been reviewed from the viewpoint of the sensitive, selective, and reliable detection of exhaled biomarker gases, and perspectives/strategies to realize breath analysis on a chip for disease diagnosis are discussed based on the concurrent design of high-performance sensing materials and miniaturized pretreatment components. Carbon-based sensing materials that show relatively high responses to NO and NH3 at low or mildly raised temperatures can be applied to the diagnosis of asthma and renal disease. Halitosis can be diagnosed by employing sensing or additive materials such as CuO and Mo that have high chemical affinities for H2S, while catalyst-loaded metal oxide nanostructure sensors or their arrays have been used to diagnose diabetes via the selective detection of acetone or by pattern recognition of sensor signals. For the ultimate miniaturization of a breath-analysis system into a tiny chip, preconditioning that includes preconcentration, dehumidification, and flow sensing needs to be either improved through the design of gas/moisture adsorbents or removed/simplified through the design of highly sensitive sensing materials that are less impervious to interference from humidity and temperature. Moreover, an abundant sensing library needs to be provided for the diagnosis of diseases (e.g. lung cancer) that are associated with multiple biomarker gases and for finding new methods to diagnose other diseases. For this aim, p-type oxide semiconductors with high catalytic activities, as well as combinatorial approaches, can be considered for the development of sensing materials that detect less-reactive large molecules, and high-throughput screening, respectively. Selectivity for a specific biomarker gas will simplify the system further. Breath analysis on a tiny chip using semiconductor chemiresistors with ultralow power consumption that is connected to the ‘Internet of Things’ will pave new roads for disease diagnosis and patient monitoring. [ABSTRACT FROM AUTHOR]

The chemical-diffusion and surface-exchange coefficients of a proton-conducting oxide, i.e., Ba(Zr 0.84 Y 0.15 Cu 0.01 )O 3−δ upon a sudden change of water-vapor pressure at a fixed oxygen partial pressure are investigated via a conductivity relaxation technique. Conductivity relaxation during the hydration/dehydration process follows typical two-fold non-monotonic behavior that can be explained by decoupled chemical diffusion of H and O. However, the temperature dependence of the measured chemical-diffusion and surface-exchange coefficients is significantly different depending on the direction of the temperature change. In this study, we attempt to identify the origin of these unusual behaviors during the conductivity relaxation experiment via thorough microstructural and compositional analyses on sample surface. [ABSTRACT FROM AUTHOR]

Herein, we report the successful synthesis and characterization of lance-shaped CuO nanostructures prepared by a simple and facile hydrothermal technique. The prepared nanostructures were examined by several techniques which revealed that the lance-shaped nanostructures are well-crystalline, grown in very high density and possessing monoclinic crystal structure. In order to develop a nano-device using synthesized nanomaterial, the prepared powder was coated on the alumina substrate with suitable electrodes and the fabricated sensor device was tested for ethanol gas. Interestingly, the gas response (resistance ratio) and response times for the fabricated devices were 9.1 and 127 s, respectively for 100 ppm of C 2 H 5 OH at 300 °C. Further, the selectivity of the developed sensing device was tested against H 2 and CO gases and interestingly, it was observed that the fabricated sensor exhibited excellent selectivity towards ethanol gas. [ABSTRACT FROM AUTHOR]

The Ruddlesden–Popper phase lanthanum nickelate, La 2 NiO 4+δ (LNO), is successfully implemented as a strontium- and cobalt-free cathode in anode-supported planar solid oxide fuel cells (SOFCs) through systematic optimization of materials, processing and structural parameters. Chemical interaction between LNO and gadolinia-doped ceria (GDC), which leads to phase decomposition of composite cathode and significant deterioration of the electrochemical performance, is prevented by lowering the processing temperature below 1000 °C. For low-temperature fabrication process, the thermo-mechanical stability at the interface is secured by modifying the powder characteristics and inserting the adhesive interlayer. The issues associated with the electrical contact and current distribution are resolved by incorporating the perovskite La 0.6 Sr 0.4 CoO 3−δ (LSC) as a current collecting layer, and the thermal stresses at the interface are relieved by constructing a gradient electrode structure. Consequently, the optimized anode-supported planar cell with an LNO-based cathode exhibits superior performance compared to the reference cell with a conventional cathode in the intermediate-temperature range, which is attributed to the enhanced interfacial process and surface reaction kinetics based on impedance analysis. [ABSTRACT FROM AUTHOR]

Co 2 (OH) 3 Cl/reduced graphene oxide (RGO) composite powders for use as anodes in lithium ion batteries were prepared directly by spray pyrolysis from a colloidal solution of graphene oxide sheets and cobalt chloride. Co 2 (OH) 3 Cl nanocrystals less than 10 nm in size were uniformly distributed throughout the spherical Co 2 (OH) 3 Cl/RGO composite powder. CoCl 2 ·6H 2 O/RGO, CoCl 2 ·6H 2 O/Co 3 O 4 /RGO, and Co 3 O 4 powders were also prepared by post-treatment of the Co 2 (OH) 3 Cl/RGO powders at 200, 300, and 400 °C, respectively, in air. The initial discharge capacities of the Co 2 (OH) 3 Cl/RGO, CoCl 2 ·6H 2 O/RGO, CoCl 2 ·6H 2 O/Co 3 O 4 /RGO, and Co 3 O 4 powder electrodes at a current density of 1000 mA g −1 were 1685, 1518, 1655, and 1046 mA h g −1 , respectively, and their discharge capacities after 200 cycles were 1186, 1030, 884, and 805 mA h g −1 , respectively. The discharge capacities of the Co 2 (OH) 3 Cl/RGO composite powder electrode for the 2nd and 600th cycles at a current density of 5000 mA g −1 were 1063 and 833 mA h g −1 , respectively. The Co 2 (OH) 3 Cl/RGO powders had smaller charge transfer resistance and faster lithium-ion diffusion rate than the other materials. [ABSTRACT FROM AUTHOR]

Yolk-shell-structured Zn-Fe-S multicomponent sulfide materials with a 1:2 Zn/Fe molar ratio were prepared applying a sulfidation process to ZnFe2O4 yolk-shell powders. The Zn-Fe-S powders had mixed sphalerite (Zn,Fe)S and hexagonal FeS crystal structures. The discharge capacities of the Zn-Fe-S powders sulfidated at 350 °C at a constant current density of 500 mA g−1 for the first, second, and fiftieth cycles were 1098, 912, and 913 mA h g−1, respectively. The powders exhibited a high discharge capacity of 602 mA h g−1 even at the high current density of 10 A g−1. The synergistic effect of yolk-shell structure and multicomponent composition improved the electrochemical properties of Zn-Fe-S powders. [ABSTRACT FROM AUTHOR]

High-temperature flame spray pyrolysis is employed for finding highly efficient nanomaterials for use in lithium-ion batteries. CoO x-FeO x nanopowders with various compositions are prepared by one-pot high-temperature flame spray pyrolysis. The Co and Fe components are uniformly distributed over the CoO x-FeO x composite powders, irrespective of the Co/Fe mole ratio. The Co-rich CoO x-FeO x composite powders with Co/Fe mole ratios of 3:1 and 2:1 have mixed crystal structures with CoFe2O4 and Co3O4 phases. However, Co-substituted magnetite composite powders prepared from spray solutions with Co and Fe components in mole ratios of 1:3, 1:2, and 1:1 have a single phase. Multicomponent CoO x-FeO x powders with a Co/Fe mole ratio of 2:1 and a mixed crystal structure with Co3O4 and CoFe2O4 phases show high initial capacities and good cycling performance. The stable reversible discharge capacities of the composite powders with a Co/Fe mole ratio of 2:1 decrease from 1165 to 820 mA h g−1 as the current density is increased from 500 to 5000 mA g−1; however, the discharge capacity again increases to 1310 mA h g−1 as the current density is restored to 500 mA g−1. [ABSTRACT FROM AUTHOR]

Abstract: The phase stability and electrical conductivity of a proton-conducting oxide, Ba(Zr0.84Y0.15Cu0.01)O3−δ (BZYCu), sintered under various atmospheres was systematically investigated. The partial pressures of oxygen and barium (P Ba) were used as the tunable experimental parameters to control the surrounding atmosphere during sintering. According to the analysis, the potentially volatile species BaCO3, formed by the decomposition of BZYCu under a CO2-containing atmosphere at around 600 °C, was found to induce barium losses by evaporation. These barium losses, and the associated Y2O3 segregation, were the decisive factor in determining the phase stability and electrical conductivity of the resulting BZYCu; both of these properties deteriorated with barium evaporation. Maintaining the optimum balance of and P Ba during sintering is crucial for minimizing Y2O3 segregation by kinetically suppressing the volatilization of barium. [Copyright &y& Elsevier]

Abstract: High-performance gas sensors prepared using p-type oxide semiconductors such as NiO, CuO, Cr2O3, Co3O4, and Mn3O4 were reviewed. The ionized adsorption of oxygen on p-type oxide semiconductors leads to the formation of hole-accumulation layers (HALs), and conduction occurs mainly along the near-surface HAL. Thus, the chemoresistive variations of undoped p-type oxide semiconductors are lower than those induced at the electron-depletion layers of n-type oxide semiconductors. However, highly sensitive and selective p-type oxide-semiconductor-based gas sensors can be designed either by controlling the carrier concentration through aliovalent doping or by promoting the sensing reaction of a specific gas through doping/loading the sensor material with oxide or noble metal catalysts. The junction between p- and n-type oxide semiconductors fabricated with different contact configurations can provide new strategies for designing gas sensors. p-Type oxide semiconductors with distinctive surface reactivity and oxygen adsorption are also advantageous for enhancing gas selectivity, decreasing the humidity dependence of sensor signals to negligible levels, and improving recovery speed. Accordingly, p-type oxide semiconductors are excellent materials not only for fabricating highly sensitive and selective gas sensors but also valuable additives that provide new functionality in gas sensors, which will enable the development of high-performance gas sensors. [Copyright &y& Elsevier]

Abstract: Protonic ceramic fuel cells (PCFCs) were successfully fabricated by using 15mol% Y-doped BaZrO3-based electrolytes that have fairly good electrical conductivity and chemical stability. In order to overcome the poor sinterability of the BaZrO3-based electrolytes, which is a critical limitation in making a thin-film electrolyte for electrode-supported PCFCs, we utilized sintering aid-assisted enhanced sintering by adding 1mol% of CuO, thereby reducing the sintering temperature of the constrained thin electrolyte on a rigid electrode substrate to below 1500°C. From the process optimization of the thin BZYCu coating on the NiO–BZYCu anode substrate, we fabricated a 10-μm-thick thin and dense electrolyte layer that exhibited an open-circuit voltage (OCV) close to that of the theoretical OCV of 0.98V. However, improving the electrochemical performance by optimizing the electrode microstructure, especially in terms of the electrochemical activity of the anode and the current-collecting efficiency of the cathode, is the major concern of forthcoming study. [Copyright &y& Elsevier]

Electromotive force (EMF) measurements using electrochemical concentration cells are often used to estimate the transport number of conducting species in ionic and mixed conductors. In this study, the proton transference number of an electrolyte based on CuO-modified Y-doped BaZrO (Ba(ZrYCu)O, BZYCu) is determined using steam concentration cells based on Wagner's theory. According to the investigation, proton concentration cells including water vapor provide good estimates of the proton transference number of the BZYCu electrolyte, showing that the number increases as the water partial pressure, P(HO), increases; the proton transference number also increases as the oxygen partial pressure P(O) decreases, owing to the relatively lower hole conductivity of BZYCu at low P(O) conditions. From the combination of proton transference number with the measured total conductivity, the proton conductivity of the BZYCu electrolyte is estimated as 0.0031 S/cm at 650 °C in wet argon atmosphere. The EMF values measured under real operating conditions of the PCFC test (fuel side, 3 % HO + hydrogen; oxidant side, dry air) are found to be increased from 0.98 to 1.08 V as the temperature decreases from 650 to 550 °C. [ABSTRACT FROM AUTHOR]

Abstract: Hierarchical and hollow oxide nanostructures are very promising gas sensor materials due to their high surface area and well-aligned nanoporous structures with a less agglomerated configurations. Various synthetic strategies to prepare such hierarchical and hollow structures for gas sensor applications are reviewed and the principle parameters and mechanisms to enhance the gas sensing characteristics are investigated. The literature data clearly show that hierarchical and hollow nanostructures increase both the gas response and response speed simultaneously and substantially. This can be explained by the rapid and effective gas diffusion toward the entire sensing surfaces via the porous structures. Finally, the impact of highly sensitive and fast responding gas sensors using hierarchical and hollow nanostructures on future research directions is discussed. [Copyright &y& Elsevier]

Abstract: Sn-precursor nanowires (NWs) were prepared by refluxing a solution containing tin oxalate (SnC2O4) and ethylene glycol. The precursor NWs were heat-treated at 600°C, which successfully transformed them into SnO2 NWs without undergoing any morphological change. The morphology of the SnO2 NWs could be manipulated either by controlling the SnC2O4 concentration or by adding easily reducible noble metal salts, such as PdCl3, AgNO3 or RuCl3·H2O. The thicker and shorter SnO2 NWs, which resulted from the use of a high SnC2O4 concentration during the preparation, showed lower gas sensitivity due to their decreased gas sensing surface area. The addition of catalytically active Pd, Ag, or Ru not only changed the gas sensitivity but also significantly shortened the gas recovery times. The gas sensing characteristics of the SnO2 NWs were related to the NW morphology and, when applicable, the catalyst used. [Copyright &y& Elsevier]

Abstract: Dependence of the electrical properties on grain-boundary plane orientation is examined by a combination of high-resolution transmission electron microscopy, impedance spectroscopy, and electron energy-loss spectrometry using two kinds of SrTiO3 Σ5 ([100]/36.8°) bicrystalline grain boundaries: symmetric (310) (18.4°/18.4°) and asymmetric (8.4°/28.4°). While the symmetric grain boundary is observed to be straight with the symmetric (310)//(310) plane orientation, the asymmetric grain boundary is faceted into symmetric (310)//(310) and (210)//(210), and asymmetric (100)//(430). Grain-boundary impedance is observed only in the asymmetric grain boundary, and the electron energy-loss spectrometry quantification indicates that the asymmetric (100)//(430) facets are more oxygen-deficient than the symmetric ones. The results suggest that the asymmetric (100)//(430) facets are the most resistive among the three different facets. [Copyright &y& Elsevier]

Abstract: The spatially-resolved local impedance can be measured by ‘Millicontact Impedance Spectroscopy (MIS)’, which involves the use of an array of sub-millimeter-scale electrodes. In stabilized zirconia and gadolinia-doped ceria electrolytes with highly resistive grain-boundaries, MIS could measure the local impedance precisely and revealed the spatially-resolved changes in the grain-interior and grain-boundary resistivity. The validity of this technique was illustrated using the examples such as the design of a new scavenger material and an analysis of the diffusion of the siliceous phase along the grain boundary. [Copyright &y& Elsevier]

Abstract: The microstructural evolution and dielectric properties of CaCu3−x Ti4O12−x (3− x =2.8–3.05) ceramics were investigated. Normal grain growth behavior was observed at Cu/Ca≤2.9, while abnormal grain growth was observed at Cu/Ca≥2.95. A CuO-rich intergranular liquid phase at Cu/Ca≥2.95 and angular grain morphology were the main reasons for abnormal grain growth. However, the abundant intergranular liquid at Cu/Ca=3.05 significantly affected the relative dielectric permittivity and dielectric loss. The CuO composition is the key parameter that determines the microstructure and dielectric properties of CCTO ceramics. [Copyright &y& Elsevier]

Abstract: Pure, 140, 500, and 2500ppmMgO-doped Al2O3 specimens were sintered at 1700°C in a vacuum with and without pre-sintering heat treatment (HT) at 800°C for 50h in air. Pre-sintering HT improved the transmittance in the visible (400–700nm) range significantly. This enhanced transmittance was explained in terms of the removal of residual pores and the homogenization of the microstructure due to the lowering of the boundary mobility as a result of the MgO addition and the suppression of local densification through a pre-coarsening step. [Copyright &y& Elsevier]

Abstract: A new composition for Li+ conducting glass with an ionic conductivity >10−6S/cm was suggested in Li2O–B2O3–V2O5 system. The maximum conductivity was found along the composition lines yLi2O–(95−y)B2O3–5V2O5 (45≤y≤47) and zLi2O–50B2O3–(50−z)V2O5 (45≤z≤48). The conductivity of the binary Li2O–B2O3 glasses with an identical Li2O content is significantly smaller than that of the ternary Li2O–B2O3–V2O5 glasses, which indicated a mixed former effect between B2O3 and V2O5. The improvement in ionic conduction was discussed in relation to the change in the glass structure. [Copyright &y& Elsevier]

A solid-state amperometric CO2 sensor was prepared by combining a NASICON (Na+ conductor, Na3Zr2Si2PO12) with a porous Na2CO3 auxiliary layer deposited on a sensing electrode. The current between sensing and counter electrodes as a function of CO2 concentration was approximately linear in the range of 200–2000 ppm at 400 °C. The device could be operated stably during the test period (60 days). The sensing characteristics and long-term stability were discussed in the light of the sensing mechanism. [Copyright &y& Elsevier]

The spatial inhomogeneity of a resistive intergranular liquid was estimated by millicontact impedance spectroscopy in a 1-mol%-Al2O3-doped 15 mol% calcia-stabilized zirconia specimen. The distribution of the intergranular liquid depended significantly upon the sintering temperature, the cooling rate and the compact density of the green body, which indicates that the present impedance technique is useful for understanding and manipulating the local grain-boundary conduction. [Copyright &y& Elsevier]

An amperometric CO2 sensor was fabricated using a Pt|NASICON (Na+ conductor, Na3Zr2Si2PO12)|Pt cell and a porous Na2CO3–BaCO3 (1:1.7 in molar ratio) auxiliary layer. The sensor with the Na2CO3–BaCO3 layer showed a faster response than that with the Na2CO3 layer, and the sensor signal was barely influenced by the humidity. When operated in an amperometric mode with an applied external electric field, the sensor could detect the CO2 concentration stably and precisely without the need for a reference gas or a reference electrode material, and the sensor signal was constant for extended test periods (60 days). The sensing mechanism and the long-term stability is discussed in terms of the amperometric operation of the sensor. [Copyright &y& Elsevier]

The effect of spark plasma sintering (SPS) on the densification of TiO2 ceramics was investigated using a nanocrystalline TiO2 powder. A fully-dense TiO2 specimen with an average grain size of ∼200 nm was obtained by SPS at 700 °C for 1 h. In contrast, a theoretical density specimen could only be obtained using conventional sintering above 900 °C for 1 h with an average grain size of 1–2 μm. [Copyright &y& Elsevier]

A solid-state amperometric CO2 sensor was fabricated by combining a Li+-ion conductor (Li2CO3–Li3PO4–Al2O3) with a porous layer and a Li2CO3 auxiliary layer deposited on sensing and counter electrodes, respectively. The Li+-ion pumping current increased linearly with increasing CO2 concentration ranging from 200 to 2000 ppm at 400 °C and the 90% response time was approximately 55 s. This sensor was able to reliably detect a small change in the CO2 concentration. [Copyright &y& Elsevier]

The distribution of the intergranular liquid phase during the sintering of 8 mol% Y2O3-stabilized ZrO2 containing 0.5 mol% of SiO2 and Al2O3 was investigated using spatially resolved impedance spectroscopy. The variation in the grain-boundary resistivity as a function of the distance from the specimen surface indicated that the liquid phase coagulates at the specimen center in the initial stages of sintering, and spreads outward upon further sintering. The liquid redistribution was also examined by transmission electron microscopy. [Copyright &y& Elsevier]

Two types of alinite cements, Mg-alinite and Zn-alinite, were synthesized using the reagent grade chemicals. Their hydration behavior was compared with ordinary Portland cement (OPC) using impedance spectroscopy (IS) and 29Si nuclear magnetic resonance (NMR) spectroscopy. The bulk resistance in the IS spectra and the intensity ratio of the hydrous (Q1 and Q2) to anhydrous (Q0) phases in the NMR spectra were estimated as the extent of hydration. The results obtained from both techniques were consistent each other. Mg-alinite had a comparable hydration rate to OPC and Zn-alinite exhibited faster hydration kinetics than Mg-alinite. [Copyright &y& Elsevier]

Recently, a novel liver-related putative tumor suppressor (LPTS), which has a growth inhibitory function in the hepatocellular carcinoma (HCC) cell line, has been identified at chromosome 8p23. To determine the relationship of the LPTS with the development or progression of HCC, we analyzed the genetic alterations and the expression pattern of the LPTS gene in a series of 80 HCCs, six dysplastic nodules, and eight large regenerating nodules, determining the genomic structures. We identified a total of seven exons, of which two were alternative, and three LPTS isoforms, short (LPTS-S), medium (LPTS-M), and long-sizes (LPTS-L). In the genetic alteration study of the LPTS gene, no mutation was detected in the large regenerating nodules, dysplastic nodules, and HCC, whereas ten (34.5%) of 29 informative cases at one or more intragenic polymorphic sites showed loss of heterozygosity (LOH). Interestingly, LOH was identified only in HCC samples with hepatitis B virus (HBV) infection and the frequency of LOH was not statistically related with histologic grade and clinical stage, suggesting that allelic loss of the LPTS gene may occur as an early event in the development of HCC, especially in the cases with HBV infection. [Copyright &y& Elsevier]

In the present work, we report the processing of ultrahard tungsten carbide (WC) nanocomposites with 6 wt% zirconia additions. The densification is conducted by the spark plasma sintering (SPS) technique in a vacuum. Fully dense materials are obtained after SPS at 1300°C for 5 min. The sinterability and mechanical properties of the WC-6 wt% ZrO2 materials are compared with the conventional WC-6 wt% Co materials. Because of the high heating rate, lower sintering temperature, and short holding time involved in SPS, extremely fine zirconia parlicles (∼100 nm) and submicrometer WC grains are retained in the WC-ZrO2 nanostructured composites. Independent of the processing route (SPS or pressureless sintering in a vacuum), superior hardness (21-24 GPa) is obtained with the newly developed WC-ZrO2 materials compared with that of the WC-Co materials (15-17 GPa). This extremely high hardness of the novel WC-ZrO2 composites is expected to lead to significantly higher abrasive-wear resistance. [ABSTRACT FROM AUTHOR]

Photoluminescence (PL) emission properties of Bi-doped Y 2 O 3 (Bi:Y 2 O 3 ) phosphor thin films were investigated depending on the oxygen content in the sputtering atmosphere to find out the optimal oxygen content for obtaining Bi:Y 2 O 3 phosphor thin film with strong PL emission intensity. PL emission intensity was greatly increased by adding a small amount of oxygen to the sputtering atmosphere. However, it was gradually decreased with further increasing the oxygen content. This behavior is thought to be due to the variation of crystallinity and surface roughness of the film depending on the oxygen content in the sputtering atmosphere. The film crystallinity showed similar behavior to PL emission intensity and the surface roughness except the case of Ar only was also decreased gradually with increasing the oxygen content. Density of point defects such as oxygen vacancy and interstitial in the film was expected to be changed according to the oxygen content in the sputtering atmosphere and also this change was considered to have an effect on the PL emission intensity of the Bi:Y 2 O 3 film. In this work, Bi:Y 2 O 3 phosphor thin film with the strongest PL emission intensity could be fabricated with the oxygen content of 10% in the sputtering atmosphere. [ABSTRACT FROM AUTHOR]

An introduction is presented in which the editor discusses various reports within the issue on topics including chemoreception, artificial olfaction and devices that are designed to mimic the mammalian sensory system.

Tin oxide (SnO2) nanotubes with a fiber-in-tube structure have been prepared by electrospinning and the mechanism of their formation has been investigated. Tin oxide-carbon composite nanofibers with a filled structure were formed as an intermediate product, which were then transformed into SnO2 nanotubes with a fiber-in-tube structure during heat treatment at 500°C. Nanofibers with a diameter of 85 nm were found to be located inside hollow nanotubes with an outer diameter of 260 nm. The prepared SnO2 nanotubes had well-developed mesopores. The discharge capacities of the SnO2 nanotubes at the 2nd and 300th cycles at a current density of 1 Ag-1 were measured as 720 and 640 mAhg-1, respectively, and the corresponding capacity retention measured from the 2nd cycle was 88%. The discharge capacities of the SnO2 nanotubes at incrementally increased current densities of 0.5, 1.5, 3, and 5 Ag-1 were 774, 711, 652, and 591 mAhg-1, respectively. The SnO2 nanotubes with a fiber-in-tube structure showed superior cycling and rate performances compared to those of SnO2 nanopowder. The unique structure of the SnO2 nanotubes with a fiber@void@tube configuration improves their electrochemical properties by reducing the diffusion length of the lithium ions, and also imparts greater stability during electrochemical cycling. [ABSTRACT FROM AUTHOR]

Pristine SnO 2 nanowires (NWs), Cr 2 O 3 -decorated SnO 2 NWs, and SnO 2 –Cr 2 O 3 core-shell nanocables (NCs) were prepared by thermal evaporation, and their gas-sensing characteristics were investigated. The decoration of discrete p-type Cr 2 O 3 nanoclusters on SnO 2 NWs increased their response to trimethylamine (TMA). Highly sensitive and selective detection of TMA was attributed to the chemical affinity and catalytic activity of Cr 2 O 3 toward TMA. In contrast, the SnO 2 –Cr 2 O 3 NCs, formed by the coating of a continuous p-type Cr 2 O 3 overlayer on SnO 2 NWs, showed negligibly low responses to all analyte gases used. The variations in gas-sensing characteristics due to configuration changes in one-dimensional SnO 2 –Cr 2 O 3 hetero-nanostructures are explained and discussed in relation to the gas-sensing mechanisms of n- and p-type oxide semiconductors. [ABSTRACT FROM AUTHOR]

Oxide chemiresistors have mostly been used to detect reactive gases such as ethanol, acetone, formaldehyde, nitric dioxide, and carbon monoxide. However, the selective and sensitive detection of volatile aromatic compounds such as benzene, toluene, and xylene, which are extremely toxic and harmful, using oxide chemiresistors remains challenging because of the molecular stability of benzene rings containing chemicals. Moreover, the performance of the sensing materials is insufficient to detect trace concentration levels of volatile aromatic compounds, which lead to harmful effects on human beings. Here, the strategies for designing highly selective and sensitive volatile aromatic compound gas sensors using oxide chemiresistors were suggested and reviewed. Key approaches include the use of thermal activation, design of sensing materials with high catalytic activity, the utilization of catalytic microreactors and bilayer structures with catalytic overlayer, and the pretreatment of analyte gases or post analysis of sensing signals. In addition, future perspectives from the viewpoint of designing sensing materials and sensor structures for high-performance and robust volatile aromatic compounds gas sensors are provided. Finally, we discuss possible applications of the sensors and sensor arrays. [ABSTRACT FROM AUTHOR]

A continuous, single-step, and large-scale preparation of Pd-catalyst-loaded SnO2 yolk-shell spheres is demonstrated. These nanostructures show an unusually high response and selectivity to methyl benzenes, such as xylene and toluene, with very low cross-responses to various interfering gases, making them suitable for precise monitoring of indoor air quality. [ABSTRACT FROM AUTHOR]

Abstract: Three different compositions of ZnO–In2O3 composite nanofibers were prepared by electrospinning, and their gas sensing characteristics were compared to those of pure ZnO and In2O3 nanofibers. All ZnO–In2O3 composite nanofibers showed high response to trimethylamine (TMA), relatively low cross-response to C2H5OH, and negligible cross-responses to CO and H2; pure ZnO or In2O3 nanofibers did not show selective detection of TMA. The maximum responses to 5ppm TMA of the ZnO–In2O3 composite nanofibers with the compositions of [Zn]:[In]=67:33, 50:50, and 33:67 by at% were 133.9 at 300°C, 82.9 at 350°C, and 119.4 at 375°C, respectively. Considering all the sensing characteristics such as gas response, selectivity, and sensing/recovering kinetics together, the operation of the ZnO–In2O3 nanofiber sensor with the composition of [Zn]:[In]=33:67 by at% at 375°C was determined to be in optimal condition to detect TMA. The significant enhancement of gas response and selectivity by the formation of composite nanofibers is discussed in relation to the variation of particle size, the formation of hetero-interfaces between ZnO and In2O3, and the combination of two sensing materials with different catalytic properties, gas adsorption behaviors, and acid–base properties. [Copyright &y& Elsevier]

Abstract: WO3 hollow spheres were prepared by ultrasonic spray pyrolysis of a citric-acid-containing precursor solution, and their trimethylamine-sensing characteristics were investigated. The WO3 hollow spheres showed a high response to 5ppm of trimethylamine (R a/R g =56.9, R a: resistance in air, R g: resistance in gas) with low cross-responses to 5ppm C2H5OH, CO, CH4, C3H8, H2, NH3, and NO2. The high gas response observed was explained by the effective electron depletion of small primary particles and the enhanced gas accessibility of hollow structures with thin and porous shells. The enhanced trimethylamine selectivity was discussed in terms of the interaction between basic analyte gas and acidic sensing materials. [Copyright &y& Elsevier]

Abstract: Punched ZnO nanobelt (NB) network sensors with strong adhesion to Au electrodes were fabricated by the vapor-phase growth of ZnS NB networks and subsequent thermal annealing. The punched ZnO NB networks showed sensitive and selective detection of trimethylamine (TMA), while no significant sensitivity or selectivity to a specific gas was observed in dense ZnO NB networks. This high TMA response can be explained by abundant chemoresistive contacts, effective electron depletion, and high surface area to volume ratio of punched ZnO NB networks. [Copyright &y& Elsevier]

Abstract: The Co3O4 nanofibers were prepared by electrospinning and their gas sensing characteristics were investigated. The Co3O4 sensors prepared by heat treatment of as-spun precursor fibers at 500 and 600°C showed well-developed one-dimensional morphologies and exhibited high responses to 100ppm C2H5OH (R g/R a =51.2 and 45.3; R g, resistance in gas; R a, resistance in air) at 301°C with negligible cross-responses to 100ppm CO, C3H8, and H2 (R g/R a =1.02–2.7). In contrast, the most of one-dimensional morphology of the Co3O4 specimen was lost and the response to 100ppm C2H5OH became significantly lower when the heat treatment temperature was increased to 700°C or when the nanofibers were ultrasonically disintegrated into primary particles. The significant decrease of the gas response was explained and discussed in relation to the gas sensing mechanism of a p-type semiconductor, the morphology of specimens, and the connecting configuration between nanoparticles and nanofibers. [Copyright &y& Elsevier]

Abstract: In inorganic semiconductor (such as CdS)-sensitized solar cells, isolated nanoparticles (including quantum dots) or Porous semiconducting layers are particularly efficient and effective in extracting charge carriers generated by solar energy, without a serious recombination among sensitizers. In this study, porously structured CdS was formed by spray pyrolysis deposition (SPD) using an excess cadmium chloride and thiourea aqueous mixture solution onto an mp-TiO2 substrate pre-heated to 450°C in an air atmosphere and subsequent washing of the excess cadmium chloride using deionized water. As expected, the power conversion efficiency of a photoelectrochemical solar cell fabricated with the porous CdS was greatly improved, to 1.71%, the highest efficiency ever reported for CdS-sensitized solar cells employing polysulfide as an electrolyte. This improvement in performance is attributed to the efficient transport of the charge carriers generated in CdS. [Copyright &y& Elsevier]

Abstract: Hierarchical and hollow In2O3 microspheres were prepared by a solvothermal self-assembly reaction and their CO sensing characteristics were compared to those of an agglomerated counterpart. Upon exposure to 10–50ppm CO at 400°C, the gas responses (R a /R g ; R a : resistance in air, R g : resistance in gas) of the hierarchical and hollow structures were 1.6–2.7 times higher than that of the agglomerated sample. In addition, their 90% responses and recovery speeds were 23 times and 7.7 times higher, respectively. Their significantly improved gas responses and sensing/recovery kinetics were concluded to be related to the nanoporous and well-aligned nanostructures, which allow effective and rapid gas diffusion toward the sensing surfaces. [Copyright &y& Elsevier]

Abstract: The Sn3O4 hierarchical microspheres self-assembled from nanosheets were prepared by a hydrothermal reaction of aqueous solution containing SnCl2·2H2O, H2C2O4, HCl, and N2H4·H2O, which were successfully transformed into nano-porous SnO2 hierarchical microspheres for gas sensor applications by heat treatment at 600°C. The morphology of building blocks within the SnO2 hierarchical spheres could be manipulated from 0-dimensional nanoparticles to 2-dimensional nanosheets by varying the amount of H2C2O4 and N2H4·H2O. The SnO2 hierarchical spheres showed both the ultra-fast response (∼1s) and high sensitivity to 50ppm C2H5OH. The dramatic improvement in gas sensing characteristics was explained by the rapid diffusion of the target gas onto the entire sensing materials through the nano-porous network of nanosheets. [Copyright &y& Elsevier]

Abstract: Various compositions of gas sensing films were prepared by the combinatorial deposition of SnO2, ZnO, and WO3 sol solutions and their gas sensing behaviors were investigated. The film composition could be manipulated conveniently via the alternate dropping of different oxide sol solutions. From the correlation between film compositions and gas sensitivities, the selective detection of C2H5OH and CH3COCH3 in the presence of CO, C3H8, H2, and NO2 could be attained. In addition, the discrimination between C2H5OH and CH3COCH3, which is a challenging issue due to their similar chemical nature, becomes possible. This research demonstrates the precise design of the sensor-material composition for the selective gas detection via the combinatorial approach. [Copyright &y& Elsevier]

Abstract: The abnormal grain growth (AGG) behavior of undoped and SiO2-doped CaCu3Ti4O12 (CCTO) ceramics were investigated. With the addition of 2wt.% SiO2, the AGG-triggering temperature decreased from 1100 to 1060°C, and the temperature for obtaining a uniform and coarse microstructure decreased from 1140 to 1100°C. The lowering of the AGG temperature by SiO2 addition was attributed to the formation of a CuO-SiO2-rich intergranular phase at lower temperature. The apparent dielectric permittivity of coarse SiO2-doped CCTO ceramics was ∼10 times higher than that of fine SiO2-doped CCTO ceramics at the frequency of 103–105 Hz. The doping of SiO2 to CCTO ceramics provides an efficient route of improving the dielectric properties via grain coarsening. The correlation between the microstructure and apparent permittivity suggests the presence of a barrier layer near the grain boundary. [Copyright &y& Elsevier]

Abstract: The CO response time of SnO2 acicular-particle-type gas sensors was shortened to a great extent using rapid microwave calcination. When SnO2 acicular particles were prepared by the slow heating (heating rate: 4.2°C/min) of a SnC2O4 precursor to the calcination temperature (500°C) using a conventional furnace, the 90% response time to 30ppm CO (t 90%(air-to-CO)) was 76s at a sensing temperature of 450°C. However, the t 90%(air-to-CO) decreased markedly down to 5–27s when the precursor was heated rapidly (heating rate: 25–100°C/min) using a microwave furnace. The significant shortening of the response time was attributed to the formation of a mesoporous structure in the SnO2 acicular particles due to rapid gas evolution during the decomposition of the SnC2O4 precursor. [Copyright &y& Elsevier]

Abstract: Porous TiO2 films were prepared by the micro-arc oxidation (MAO) of Ti plates, and their CO sensing properties at low concentrations (5–100ppm) were investigated as an application for an air quality control sensor. The obtained rutile films exhibited the maximum CO gas response at 350°C, which is typical for semiconductor-type gas sensors, and the R a/R g was ∼1.6 for 10ppm CO (R a: resistance in air, R g: resistance in a sample gas). The magnitude of the gas response increased almost linearly with increasing the CO concentration from 5 to 100ppm. The CO sensing performance of the TiO2 sensor in the presence of humidity was investigated and compared with that of a SnO2 sensor. [Copyright &y& Elsevier]

Abstract: A new approach to improve the grain-boundary conduction in 10 mol% gadolinia-doped ceria (GDC) without any additives was suggested. The grain-boundary conductivity of GDC specimen containing 500 ppm of SiO2 was increased ∼4 times by post-sintering heat-treatment (HT) at 1350 °C for 20 h. The grain-boundary conductivity showed the maximum at HT temperature of 1350 °C and enhanced with increasing HT time from 0 to 20 h. The mechanism for scavenging resistive siliceous phase by post-sintering HT was investigated with the variation of HT temperatures, HT times, and HT schedules. [Copyright &y& Elsevier]

Abstract: A highly sensitive H2 gas sensor was prepared by the thermal oxidation of a Ti plate at 600–1000°C. The H2 sensitivity (the ratio of the resistances between N2 and 1.0% H2 balanced with N2) of the oxidized TiO2 increased exponentially with increasing oxidation temperature up to 900°C but decreased drastically at 1000°C. The maximum sensitivity to 1.0% H2 was 1.2×106, which is the highest value reported in the literature. The mechanism for the enhanced H2 sensing was examined by investigating the phase, thickness and morphology of the oxidized TiO2 layer and the sensor response time. The thermally oxidized specimens exhibited an approximately linear dependence of the sensitivity on the H2 concentrations from 50 to 10,000ppm, and excellent sensitivity (∼103) was still obtained in the sensor operated at temperatures as low as 150°C. [Copyright &y& Elsevier]

Abstract: Among different RNA amplification methods, T7 RNA polymerase-based in vitro transcription (IVT) that generates antisense RNA is most common in DNA microarray protocol. However, despite the fact that cRNA targets labeled during IVT are feasible for spotted-oligonucleotide microarray (spotted-oligoarray) hybridization due to complementary sequence of single-stranded oligonucleotide probe, no systemic assessment for the use of amplified cRNA targets has been reported for spotted-oligoarrays. In this investigation, we have compared the hybridization performance of amplified cRNA targets with that of cDNA targets from total RNA(T-RNA) using spotted-oligoarrays containing 18,864 genetic elements. Under the optimized hybridization conditions, we found that 86% of oligonucleotide probes were reproducibly detected by both cDNA and cRNA target protocols. In addition, cRNA targets generated by two-rounds of amplification of 10ng T-RNA were concordant with first-round cRNA targets generated from 100ng T-RNA by 0.858 of correlation coefficient. Taken together, we demonstrated that cRNA targets from very scant RNA amount could successfully be applied on spotted-oligoarrays, and hopefully this will facilitate the application of much smaller amount of source material based on the high-fidelity and improved target preparation of microarrays. [Copyright &y& Elsevier]

Abstract: The grain-boundary resistivity of CaO·2SiO2-in-diffused 8 mol%-yttria-stabilized zirconia (8YSZ-CS) or SiO2-in-diffused 8 mol%-yttria-stabilized zirconia (8YSZ-S) was determined by local impedance spectroscopy using submillimeter-scale electrodes. During sintering, a liquid formed at the top of the 8YSZ penetrates or diffuses into the 8YSZ interior. For CaO·2SiO2-in-diffused 8YSZ, the grain-boundary resistivity of the specimen surface was observed to be 150 times greater than that of the interior, and grain growth was enhanced near the surface region. In contrast, for SiO2-in-diffused 8YSZ, the near-top surface region did not show enhanced grain growth and its grain-boundary resistivity was only nine times higher than that of the specimen interior. [Copyright &y& Elsevier]

The grain-boundary resistivity of CaSi2O5-dropped 8 mol%-yttria-stabilized zirconia (8YSZ) was determined by impedance spectroscopy using sub-millimeter-scale electrodes. During sintering, a liquid that formed at the top surface of the specimen penetrated into the 8YSZ and induced enhanced grain growth near the surface region. The grain-boundary resistivity of the specimen surface was observed to be 150 times higher than that of the interior. The deterioration of the grain-boundary conductivity was explained in terms of the presence of an intergranular siliceous phase. [Copyright &y& Elsevier]

Low-temperature anneals (1200 °C for 40 h) of 8 mol% yttria-stabilised zirconia, prior to the samples being sintered at 1500 °C, had the effect of improving the ionic conductivity of the specimens. The presence of SiO2 in the specimens was shown to be detrimental, however. Irrespective of the SiO2 content, this type of heat treatment also leads to improvements in conductivity. Extensive microstructural analysis provided indication of the mechanism of this phenomenon. This included selective formation of zircon, relief of sintering strain leading to the formation of coherent grain boundaries and segregation effects. [Copyright &y& Elsevier]